ADMINISTRATIVE LAW – appeal from Civil and Administrative Tribunal – whether decision made by validly constituted tribunal – four-member tribunal was constituted for the purposes of the hearing – whether principal member could separately and simultaneously constitute herself as the tribunal to decide legal questions – single member of a multi-person tribunal which has already been constituted not authorised to constitute himself or herself as the tribunal on unstated informal basis or to make a decision unilaterally without recourse to the balance of the tribunal – decision void